The present invention relates generally to image and video processing, and more particularly to contrast enhancement.
Contrast enhancement is used to improve the picture quality of digital video and is often implemented using video processors. Although many image processing techniques exist for contrast enhancement, they are often unsuitable for an ASIC implementation because of their computational complexity and/or storage requirements. Additionally, many image processing techniques might not work for video, because the picture is continuously changing and many algorithms may be prone to artifacts like contouring and saturation of gray levels.
Because contrast enhancement is usually performed in a color space that separates brightness information from color, most algorithms operate on data in formats such as YCbCr, HSV, and the like. For video applications, the YCbCr format is typically used because it is the industry standard for video transmission and storage. The YCbCr format is also typically easier to convert to and from RGB than from HSV. The ease in conversion is important because the final display is usually configured to accept data in RGB format.
Copending, commonly-assigned U.S. patent application Ser. No. 11/295,750, filed Dec. 7, 2005 and hereby incorporated by reference herein in its entirety, describes histogram-based video contrast enhancement technique in which a histogram of pixel luminance for an image is divided into a plurality of regions that are processed independently using equalization techniques. However, one effect of using equalization on a histogram that has been broken into regions is that the effect of a sharp peak in one region of the histogram may distort the results for that region.
It would be desirable to be able to provide video contrast enhancement that is less affected by sharp peaks in the luminance histogram.